The usual process for dewetting solid surfaces consists in immersing the wet substrate in an organic solution of an ionic or non-ionic surface-active agent. Until recently, the organic solvent commonly used was 1,1,2-trichloro-1,2,2-trifluoroethane (CFC 113) but its use has been banned because of its harmful effect on the stratospheric ozone layer.
The use of 1-chloro-1,1-difluoroethane (HCFC 141b), provided as substitute for CFC 113 in dewetting compositions, is already regulated and before long it will no longer be possible to use this compound.
To replace CFC 113 and HCFC 141b, the use has been envisaged of fluorinated hydrocarbons which, like 1,1,1,3,3-pentafluorobutane (365 mfc), 1,1,1,2,2,4,4-heptafluorobutane (347 mcf), (perfluorobutyl)ethylene (C4F9CH═CH2), 1H-perfluorohexane, n-perfluorohexane (PF 5060) or 1,1,1,2,3,4,4,5,5,5-decafluoropentane (43-10 mee), and perfluoro(methylmorpholine) (PF 5052), have no effect on the stratospheric ozone layer (zero ODP), do not exhibit a flash point and, as is shown in the following table, possess physical characteristics which are similar to those of CFC 113 and HCFC 141b.
SurfaceRelativeBoiling pointtension atdensity atSolvent(° C.)25° C. (mN/m)20° C.CFC 11347.617.71.57HCFC 141b3219.51.23365 mfc4016.21.27347 mcf33.314.21.42C4F9CH═CH25913.61.46C6F13H71131.70PF 506056121.68PF 505250131.7043-10 mee5414.11.58
However, the replacement of CFC 113 or of HCFC 141b by a fluorinated hydrocarbon such as those mentioned above is unsatisfactory because ionic-surface-active agents, which are most often used in dewetting compositions, are insoluble therein. Non-ionic surface-active agents are soluble in these fluorinated hydrocarbons but their dewetting effectiveness is often unsatisfactory.
To solve this problem in the case of 365 mfc, provision has been made, in the publication of Patent JP 05-168805, for the addition of a cosolvent chosen from alcohols, ketones, alkanes and ethers. However, when the cosolvent is an alcohol comprising 1 to 3 carbon atoms, or a ketone, it is rapidly removed with the water, causing the rapid precipitation of the surface-active agent. As regards alkanes and ethers, they exhibit a flash point, which presents a safety problem for dewetting plants.